1. Field of the Invention
The present invention relates to a laminated electronic part for use in electronic apparatuses, and more particularly to a laminated electronic part to be mounted in modules, semiconductor packages, hybrid ICs or the like for use in mobile communication equipment.
2. Description of the Related Art
A conventional laminated electronic part is disclosed in Japanese Patent Laid-Open No. 6-32382. The construction of the conventional laminated electronic part will be explained with reference to FIG. 2.
Referring to FIG. 2, reference numeral 21 denotes a laminated electronic part comprising a first layer 22 and a second layer 23 with a third layer 24 made of a thick-film glass or the like sandwiched between them.
The first layer 22 is formed by laminating a plurality of high dielectric-constant sheets (not shown) formed of ceramics having a relatively high dielectric constant, and has a shape having an obverse surface 22a, a reverse surface 22b, and sides (not shown) which are continuous with the obverse surface 22a and the reverse surface 22b. Provided inside the first layer 22 are electrodes 25 and 26 which constitute capacitor parts, each of which functions as a circuit element, and through-conductors 27 and 28 which are extended to the obverse surface 22a and the reverse surface 22b. The electrodes 25 and 26 are formed by providing conductors on the surfaces of the high dielectric-constant sheets which constitute the first layer 22. The through-conductors 27 and 28 are formed of conductors inside through-holes which go through the high dielectric-constant sheets along the thickness direction thereof and are continuous along the direction in which the high dielectric-constant sheets are laminated.
The second layer 23 is formed by laminating a plurality of low dielectric-constant sheets (not shown) formed of ceramics having a relatively low dielectric constant, and has a shape having an obverse surface 23a, a reverse surface 23b, and sides (not shown) continuous with the obverse and reverse surfaces. Provided inside the second layer 23 are electrodes 29 and 30 which constitute capacitor parts, each of which functions as a circuit element, and through-conductors 31 and 32 which are extended to the obverse surface 23a and the reverse surface 23b. The electrodes 29 and 30 are formed by providing conductors on the surfaces of the low dielectric-constant sheets which constitute the second layer 23. The through-conductors 31 and 32 are formed of conductors inside through-holes which go through the low dielectric-constant sheets along the thickness direction thereof and are continuous in the direction in which the low dielectric-constant sheets are laminated.
Further, another electronic part 33 is mounted on the surface 23a of the second layer 23, and the electronic part 33 is connected to the through-conductors 31 and 32 via terminals 34.
The first layer 22 and the second layer 23 are joined to each other with the third layer 24 sandwiched therebetween with their reverse surfaces 22b and 23b as the joining surfaces. The through-conductor 27 and the through-conductor 31 are directly connected to each other, and the through-conductor 28 and the through-conductor 32 are connected to each other via a surface conductor 35 formed by a conductor on the reverse surface 23b of the second layer 23. Another conductor is provided adjacent to the surface conductor 35, and thus surface conductor 36 is formed. The surface conductor 36 is connected to another circuit element (not shown) or the like, and thus a circuit is formed.
The laminated electronic part 21 constructed in the above-described way is mounted on a printed circuit board (not shown) with the surface 22a of the first layer 22 as the mounting surface, and is connected to the circuit wiring (not shown) on the printed circuit board.
In the laminated electronic part 21 constructed as described above, however, since the surface conductor 35 is formed on the reverse surface 23b of the second layer 23, the surface conductor 35 and the electrodes 29 face each other through a dielectric (low dielectric-constant) sheet, causing floating capacitance between them. Also, since the surface conductor 35 and the surface conductor 36 are adjacent to each other on the dielectric (low dielectric-constant) sheet, floating capacitance is caused to occur between them. Due to the influence of these floating capacitances, desired circuit characteristics cannot be obtained in the laminated electronic part 21, and there is a risk that the laminated electronic part 21 cannot be put into practical use.
The surface conductor 35 and the electrode 29, and the surface conductors 35 and 36, must be separated from each other in order to prevent an occurrence of such floating capacitance, which reduces freedom of design. For this reason, problems arise. For example, high density mounting is difficult to achieve.